CN114089409A - Detector correction method and system - Google Patents
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Abstract
The embodiment of the specification provides a detector correction method, which comprises the steps of obtaining an output value of a detector, wherein the output value is related to a radiation photon energy value received by the detector; acquiring correction information, wherein the correction information is used for correcting signal output nonlinearity of a photoelectric sensor of a detector; determining a correction value for the output value based on the correction information; based on the correction values, a detector spectrum is determined, wherein the detector spectrum represents a relationship between an energy value of the radiation photon and a count of the radiation photon.
Description
Technical Field
The present disclosure relates to the medical field, and in particular, to a method and a system for calibrating a detector.
Background
An Emission Computed Tomography (ECT) detector is a detection device for measuring or detecting energy of radiation photons, and is widely applied in the field of nuclear medicine, and the ECT detector is used in Positron Emission Tomography (PET)/Single Photon Emission Computed Tomography (SPECT) and the like. Taking PET as an example, the detector of the PET is usually composed of a scintillator radiation detector, which utilizes the property of radiation light that generates fluorescence after energy deposition in a scintillation crystal, and combines with a photosensor to indirectly measure the energy of radiation photons in the form of an electrical signal. In use, the energy spectrum of the detector needs to be acquired to obtain the energy of the detected ray, the whole detector needs to be corrected due to the nonlinearity of the signal output of the photoelectric sensor used by the detector, so that the energy spectrum obtained by measurement is in direct proportion distribution, and the analyzed crystal is usually subjected to direct energy calibration on the whole detector level, so that the energy spectrum is obtained. The obtained energy spectrum is not accurate enough due to incomplete consideration of the nonlinear relation of all components of the detector, and the space resolution and energy resolution capability of the detector are reduced.
Accordingly, it is desirable to provide a detector calibration method and system.
Disclosure of Invention
One of the embodiments of the present specification provides a method for calibrating a detector, the method including: obtaining an output value of the detector, the output value being related to the radiant photon energy value received by the detector; acquiring correction information, wherein the correction information is used for correcting signal output nonlinearity of a photoelectric sensor of the detector; determining a correction value for the output value based on the correction information; based on the correction value, a detector spectrum is determined, the detector spectrum representing a relationship between an energy value of the radiation photon and a count of the radiation photon.
One of the embodiments of the present specification provides a detector calibration system, which includes an output value acquisition module, a calibration information acquisition module, a calibration value determination module, and an energy spectrum determination module; the output value acquisition module is used for acquiring an output value of the detector, and the output value is related to the radiant photon energy value received by the detector; the correction information acquisition module is used for acquiring correction information, and the correction information is used for correcting the signal output nonlinearity of the photoelectric sensor of the detector; the correction value determining module is used for determining a correction value of the output value based on the correction information; the energy spectrum determination module is to determine a detector energy spectrum based on the correction value, the detector energy spectrum representing a relationship between an energy value of the radiation photon and a count of the radiation photon.
One of the embodiments of the present specification provides a detector calibration apparatus, which includes a processor, and the processor is configured to execute the detector calibration method.
One of the embodiments of the present specification provides a computer-readable storage medium, which stores computer instructions, and when the computer reads the computer instructions in the storage medium, the computer executes the probe calibration method.
Drawings
The present description will be further explained by way of exemplary embodiments, which will be described in detail by way of the accompanying drawings. These embodiments are not intended to be limiting, and in these embodiments like numerals are used to indicate like structures, wherein:
FIG. 1 is a schematic diagram of an application scenario of a detector calibration system according to some embodiments of the present description;
FIG. 2 is a schematic diagram of a detector calibration system according to some embodiments herein;
FIG. 3 is an exemplary flow chart of a method of detector calibration shown in accordance with some embodiments of the present description;
FIG. 4 is a schematic illustration of a detector calibration method according to some embodiments herein;
FIG. 5 is a schematic diagram of a crystal array unit and its SiPM array unit shown in accordance with some embodiments herein;
FIGS. 6A and 6B are schematic flow maps of SiPMs of different pixel sizes according to some embodiments of the present description;
FIG. 7 is a schematic illustration of a calibration curve for a SiPM shown in accordance with some embodiments herein;
FIGS. 8A and 8B are schematic flow maps of SiPMs before and after calibration according to some embodiments of the present disclosure;
fig. 9A, 9B are crystal energy spectra of sipms before and after correction, shown in some embodiments herein.
Detailed Description
In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only examples or embodiments of the present description, and that for a person skilled in the art, the present description can also be applied to other similar scenarios on the basis of these drawings without inventive effort. Unless otherwise apparent from the context, or otherwise indicated, like reference numbers in the figures refer to the same structure or operation.
It should be understood that "system", "apparatus", "unit" and/or "module" as used herein is a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, other words may be substituted by other expressions if they accomplish the same purpose.
As used in this specification and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural, unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
Flow charts are used in this description to illustrate operations performed by a system according to embodiments of the present description. It should be understood that the preceding or following operations are not necessarily performed in the exact order in which they are performed. Rather, the various steps may be processed in reverse order or simultaneously. Meanwhile, other operations may be added to the processes, or a certain step or several steps of operations may be removed from the processes.
FIG. 1 is a schematic diagram of an application scenario of a detector calibration system according to some embodiments of the present disclosure.
In some application scenarios, the detector calibration system may include a processing device and a medical imaging device, and the detector calibration system may implement the method and/or process disclosed in this specification by the processing device, etc. to achieve spectral calibration of the detector in the medical imaging device, thereby achieving accurate measurement of the energy of the detector, achieving effective treatment of the patient, and reducing adverse effects on the body of the patient.
As shown in fig. 1, in some embodiments, the system 100 may include a medical imaging device 110, a processing device 120, a storage device 130, a terminal 140, and a network 150.
The medical imaging apparatus 110 is a device for reproducing the internal structure of a human body as an image by using different media in medicine. In some embodiments, the medical imaging device 110 may be any medical device that includes a detector to image or treat a designated body part of a patient with a radionuclide, such as SPECT, PET-CT, SPECT-CT, or the like. The medical imaging device 110 is provided above for illustrative purposes only and is not intended to be limiting in scope. A detector in the medical imaging device 110 may receive radiation from the radiation source and meter the received radiation. In some embodiments, medical imaging device 110 may send data and information related to the detector, e.g., a photon energy value of radiation received by the detector, an output value of the detector, etc., to processing device 120. In some embodiments, at least some parameters of the medical imaging device 110 may be stored in the storage device 130, and these parameters may be associated with a probe, such as a probe's energy spectrum, flood map (flood map), and the like. The medical imaging device 110 can receive instructions and the like sent by the doctor through the terminal 140 and perform relevant operations according to the instructions, such as irradiation imaging and the like. In some embodiments, medical imaging device 110 may exchange data and/or information with other components in system 100 (e.g., processing device 120, storage device 130, terminal 140) via network 150. In some embodiments, the medical imaging device 110 may be directly connected to other components in the system 100. In some embodiments, one or more components (e.g., processing device 120, storage device 130) in system 100 may be included within medical imaging device 110.
The processing device 120 may process data and/or information obtained from other devices or system components and perform the detector calibration methods shown in some embodiments of the present description based on the data, information, and/or processing results to perform one or more of the functions described in some embodiments of the present description. For example, the processing device 120 may obtain a true energy spectrum of the detector based on the detector-related data and information of the medical imaging device 110 to correct for the non-linearity of the detector and obtain a true energy value received by the detector. For another example, the processing device 120 may generate a correction formula for the photosensor based on the detector sampling data of the medical imaging device 110 for correcting the input energy value of the photosensor. In some embodiments, the processing device 120 may send the processed data, such as the actual energy spectrum of the detector, the calibration formula of the photo sensor, the flood map of the detector, etc., to the storage device 130 for storage. In some embodiments, the processing device 120 may obtain pre-stored data and/or information from the storage device 130, such as calibration formulas of the photo-sensor, flood map of the detector, etc., for performing the detector calibration methods shown in some embodiments herein, such as obtaining the true energy spectrum of the detector, etc.
In some embodiments, the processing device 120 may include one or more sub-processing devices (e.g., single core processing devices or multi-core processing devices). By way of example only, the processing device 120 may include a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), an Application Specific Instruction Processor (ASIP), a Graphics Processing Unit (GPU), a Physical Processing Unit (PPU), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), a programmable logic circuit (PLD), a controller, a micro-controller unit, a Reduced Instruction Set Computer (RISC), a microprocessor, or the like or any combination thereof.
The terminal 140 may control the operation of the medical imaging device 110. The doctor may issue an operation instruction to the medical imaging apparatus 110 through the terminal 140, so that the medical imaging apparatus 110 performs a specified operation, for example, irradiation imaging of a specified body part of the patient. In some embodiments, the terminal 140 may be instructed to cause the processing device 120 to perform the detector calibration method as shown in some embodiments herein. In some embodiments, the terminal 140 can receive the corrected detector input energy value from the processing device 120 so that the physician can accurately determine the radiation dose value to which the patient is subjected for effective and targeted examination and/or treatment of the patient. In some embodiments, the terminal 140 may be one or any combination of a mobile device 140-1, a tablet computer 140-2, a laptop computer 140-3, a desktop computer, or other device having input and/or output capabilities.
The network 150 may connect the various components of the system and/or connect the system with external resource components. The network 150 enables communication between the various components and with other components outside the system to facilitate the exchange of data and/or information. In some embodiments, one or more components of interface system 100 (e.g., medical imaging device 110, processing device 120, storage device 130, terminal 140) may send data and/or information to other components via network 150. In some embodiments, the network 150 may be any one or more of a wired network or a wireless network.
It should be noted that the foregoing description is provided for illustrative purposes only, and is not intended to limit the scope of the present description. Many variations and modifications may be made by one of ordinary skill in the art in light of the teachings of this specification. The features, structures, methods, and other features of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. For example, the processing device 120 may be based on a cloud computing platform, such as a public cloud, a private cloud, a community and hybrid cloud, and so forth. However, such changes and modifications do not depart from the scope of the present specification.
FIG. 2 is a schematic diagram of a detector correction system according to some embodiments herein.
As shown in fig. 2, in some embodiments, the detector correction system 200 may include an output value acquisition module 210, a correction information acquisition module 220, a correction value determination module 230, and a power spectrum determination module 240.
In some embodiments, the output value obtaining module 210 may be configured to obtain an output value of the detector, where the output value is related to an amount of radiant photon energy received by the detector, and the amount of radiant photon energy received by the detector may be used to represent the amount of radiant energy received by the detector, i.e., the detector input energy value.
In some embodiments, the correction information obtaining module 220 may be configured to obtain correction information, which may be used to correct signal output nonlinearity of a photosensor of the detector, so as to convert an input energy value and an output value of the detector into a linear relationship.
In some embodiments, the correction information may be expressed as a correction formula, i.e., formula 1
ADC＝h(g(Nph(E))) (1)
Wherein the ADC represents a detector output value; n is a radical ofph(E) Representing a relationship between an energy value E of a radiation photon received by the detector and a number of luminescent photons generated by a crystal of the detector based on the radiation photon; g (N)ph) Represents a non-linear relationship between the electrical signal produced by the photosensor based on the luminescent photons and the number of luminescent photons; h (g) represents the relationship between the electrical signal and the output value.
In some embodiments, the correction information acquisition module 220 may include a sampling unit 221 and a fitting unit 222. The sampling unit 221 may be configured to obtain multiple sets of sampling values of the detector, where each set of sampling values may include an input energy sampling value of the detector and an output sampling value of the detector corresponding to the input energy sampling value; the fitting unit 222 is configured to fit a plurality of sets of sample values to determine correction information. In some embodiments, the sampling unit 221 may acquire, for each of the photosensors, a plurality of sets of input energy values and detector output values corresponding to the input energy values under preset measurement conditions. In some embodiments, the correction information may be a correction formula, and the fitting unit 222 may fit the sets of sample values using various data fitting methods including interpolation, regression, and the like to determine coefficients in the correction formula, thereby determining the correction formula.
In some embodiments, the correction value determination module 230 may be configured to determine a correction value for the detector output value based on the correction information. The correction value determination module 230 may back-derive the output value of the detector to a correction value of the output value based on a correction formula.
In some embodiments, the energy spectrum determination module 240 may include a correction coefficient determination unit 241 and an energy spectrum determination unit 242. The correction coefficient determination unit 241 is configured to determine a crystal correction coefficient of the detector based on the correction value of the detector output value; the spectrum determination unit 242 is configured to determine a detector spectrum based on the crystal correction factor.
In some embodiments, the detector may include a plurality of crystals, and the correction coefficient determination unit 241 may determine a crystal correction coefficient for each crystal, and the crystal correction coefficient may be used to correct the energy spectrum of the crystal to obtain a true energy spectrum of the crystal. In some embodiments, for each crystal, the correction coefficient determination unit 241 may determine a first crystal energy spectrum based on the correction values, the first crystal energy spectrum representing a relationship between a count of radiation photons received by the crystal and the corresponding correction values; then, acquiring an energy value corresponding to an energy peak on the first crystal energy spectrum and a corresponding correction value; and determining a crystal correction coefficient based on the energy value corresponding to the energy peak and the corresponding correction value.
In some embodiments, the correction coefficient determination unit 241 may use an acquisition target map for determining the position of the crystal receiving the radiation photons, based on the correction values; based on the target spectrum, a first crystal energy spectrum for each crystal is determined. In some embodiments, the target map may be a flood map of the probe.
In some embodiments, for each crystal, the energy spectrum determination unit 242 may determine a second crystal energy spectrum based on the crystal correction coefficient and the first crystal energy spectrum, the second crystal energy spectrum representing a relationship between an energy value of a radiation photon received by the crystal and a count of the corresponding radiation photon; the detector energy spectrum is then determined based on the second crystal energy spectrum of all the crystals of the detector.
FIG. 3 is an exemplary flow chart of a method of detector calibration shown in accordance with some embodiments of the present description.
As shown in fig. 3, the process 300 includes the following steps. In some embodiments, flow 300 may be performed by processing device 120.
In step S310, an output value of the detector is obtained. In some embodiments, step S310 may be performed by the output value acquisition module 210.
The output value is related to the radiation energy received by the detector, for example, an output value of an Analog to Digital Converter (ADC) of the detector. In some embodiments, the output value of the detector may be related to the amount of radiant photon energy received by the detector. The crystal in the detector can receive radiation photons emitted by the radioactive source and then emit luminescent photons, the luminescent photons are received by the photoelectric sensor in the detector and then converted into electric signals, and the electric signals are converted into corresponding ADC values through the analog-to-digital converter in the detector and then output.
In some embodiments, the energy value of the radiation photon may be a radioactive source gamma ray energy value. In some embodiments, the output value acquisition module 210 may acquire an ADC value output by the detector as the output value of the detector.
In step S320, correction information is acquired. In some embodiments, step S320 may be performed by the correction information acquisition module 220.
The correction information is information for correcting the output value of the detector, and for example, the correction information may include a correction formula, a correction coefficient, an offset value, and the like. There is a non-linear relationship between the input (e.g., luminescence photons) and the output (e.g., electrical signal based on luminescence photons) of the detector's photosensor. In some embodiments, the correction information is used to correct for signal output non-linearities of the photo-sensor of the detector, and the input and output of the photo-sensor through the correction may be represented as a linear relationship.
In some embodiments, the correction information may include a correction formula that may represent a relationship between an energy input value of the detector and an output ADC value of the detector.
In some embodiments, a plurality of parameters may be included in the correction formula, which may be determined based on the input and output of the detector.
In some embodiments, the correction information may be expressed as ADC ═ h (g (N)ph(E) ) where ADC represents the detector output value; n is a radical ofph(E) Representing a relationship between an energy value E of a radiation photon received by the detector and a number of luminescent photons generated by a crystal of the detector based on the radiation photon; g (N)ph) Represents a non-linear relationship between the electrical signal produced by the photosensor based on the luminescent photons and the number of luminescent photons; h (g) represents the relationship between the electrical signal and the output value.
In some embodiments, the correction information obtaining module 220 may obtain the correction information by comparing N of the correction informationph(E) And h (g) assuming a linear relationship, determining a plurality of parameters in the calibration equation, and determining the relationship between the energy value E and the ADC value. For example only, the relation may be expressed as ADC ═ α (1-e)-βE) Where α and β are the parameters to be determined and e is the natural logarithm.
In some embodiments, after acquiring the detector output values, the correction information acquisition module 220 may acquire the correction information in various ways, such as sampling the detector data, based on historical statistical data, using a machine learning model, and so forth. In some embodiments, the calibration information acquisition module 220 may pre-acquire calibration information before the probe is operated and then store the calibration information in a storage device. For more details on how to obtain the correction information, reference may be made to the description of fig. 4, which is not repeated here.
In step S330, a correction value of the output value is determined based on the correction information. In some embodiments, step S330 may be performed by the correction value determining module 230.
In some embodiments, the correction value determining module 230 may correct the output value of the detector based on the correction information, e.g., a correction formula, and determine a correction value of the output value. In some embodiments, the correction value may be taken as the true input energy value of the detector. Since the real energy input value and the real ADC value are theoretically linear, the real input energy value of the detector, i.e. the correction value, can be equivalently used as the real ADC value, i.e. the ADC value of the linear output of the detector. In some embodiments, the actual input energy value of the detector, i.e. the correction value, may be used as a correction value for the actual output value of the detector.
In some embodiments, the correction value determining module 230 may obtain a calculation formula of the output value by performing a reverse-extrapolation on the correction formula, and substitute the output value of the detector into the calculation formula, and the obtained output value is used as the correction value.
Step S340, determining a detector energy spectrum based on the correction value. In some embodiments, step S340 may be performed by the energy spectrum determination module 240.
In some embodiments, the energy spectrum may represent a correspondence between information related to the energy of the radiation photon and the radiation photon count. For example, the energy spectrum may represent a correspondence between a value associated with the ADC output and the radiation photon count. As shown in the energy spectrum 900-1 of fig. 9A, the abscissa may be the ADC value and the ordinate is the received radiation photon count. As another example, the energy spectrum may represent a correspondence between an energy value of a radiation photon and a radiation photon count having a corresponding energy value. As shown in the energy spectrum 900-2 of fig. 9B, the abscissa may be the energy value of the radiation photon and the ordinate is the radiation photon count.
In some embodiments, the detector spectrum may represent a relationship between an energy value of a radiation photon received by the detector and a count of radiation photons having a corresponding energy value. In some embodiments, the detector spectrum may include a spectrum corresponding to each crystal in the detector.
In some embodiments, the spectrum determination module 240 may determine a crystal correction coefficient for the detector based on the correction value, and determine the detector spectrum based on the crystal correction coefficient. For more details on how the detector spectrum is determined based on the correction values, reference may be made to the description of fig. 4, which is not repeated here.
Some embodiments of the present disclosure obtain the energy spectrum of the detector by respectively calibrating the photoelectric sensor and the crystal of the detector, and specially calibrate the nonlinearity of the signal output of the photoelectric sensor, which improves the problem of low resolution of the crystal due to the nonlinearity of the photoelectric sensor, so that the nonlinearity of the detector is calibrated more accurately and comprehensively, the accuracy of the energy spectrum of the detector is improved, and the spatial resolution and the energy resolution of the detector are improved to a certain extent.
FIG. 4 is a schematic diagram of a detector calibration method according to some embodiments herein.
As shown in the flow 400 of fig. 4, correction information, i.e., a correction formula 410, may be acquired by the correction information acquisition module 220, and the correction information may be used to correct signal output nonlinearity of the photosensor of the detector.
By way of example only, in some detectors, a SiPM, a solid-state photosensor composed of an array of APD (photodiode) pixels of micron size and operating in avalanche mode, is used as the core photosensor device. The SiPM has a saturation effect, and for the SiPMs with the same photosensitive area and different APD pixel sizes, the larger the pixel size, the more serious the saturation effect is, and the more unfavorable the flood map quality, the spatial resolution and the energy resolution of the detector are.
Taking two sipms with pixel sizes of 30um (micrometer) and 75um respectively as an example, the saturation effect of 75um is severe, and the spatial resolution and the energy resolution are low. Fig. 5 is a schematic diagram of a crystal array unit and its SiPM array unit according to some embodiments of the present disclosure, in which a 3 × 3 crystal array is coupled to a 2 × 2 SiPM array as a detector unit, a0 is one of the crystal units, and B0, B1, B2, and B3 are SiPM units. Fig. 6A and 6B are schematic diagrams of flood maps of sipms of different pixel sizes according to some embodiments of the present disclosure, and flood maps for resolving crystal positions can be obtained by using the two sipms as shown in fig. 6A and 6B. It can be seen that 9 cluster points in the flood map calculated by 30um SiPM in fig. 6A are more concentrated respectively, and the crystal analysis position is more accurate, while 9 cluster points in the map calculated by 75um SiPM in fig. 6B are looser respectively, and the interference between clusters is more serious, and the unfavorable position is analyzed. Therefore, the following detector module, which is constructed with SiPMs of 75um pixel size, is taken as a calibration example.
In some embodiments, the sampling unit 221 may obtain a plurality of sets of sample values of the detector, each set including an input energy sample value of the detector and an output sample value of the detector corresponding to the input energy sample value.
In some embodiments, the sampling unit 221 may collect, for each of the photosensors, multiple sets of energy spectrum samples corresponding to different input energy values and corresponding output sample values under preset measurement parameters, and determine each set of sample values according to an energy peak of each of the multiple sets of energy spectrum samples.
The predetermined measurement parameters may be parameters of the detector and its components, which are predetermined and related to the measurement values, and may be property parameters, operation parameters, such as crystal size, crystal cross-sectional area, photosensor operation voltage, and the like. In some embodiments, the predetermined measurement parameter may be that the crystal used for measurement is the same size as the crystal cross-sectional area of the detector, and the voltage of the photoelectric sensor is fixed, typically the working voltage of the photoelectric sensor. In some embodiments, the sampled values may be obtained by sampling directly on the detector that requires correction.
As shown in FIG. 4, in some embodiments, gamma spectra of a plurality of radiation sources with different energy gamma rays can be respectively collected on a photoelectric sensor (detector crystal unit) which is coupled with a certain fixed voltage and takes the cross section area consistent with the size of the detector crystal as a correction crystal, and [ E ] can be obtained0,ADC0],[E1,ADC1]...[En-1,ADCn-1]And (4) waiting n groups of ADC values of energy corresponding to energy peaks in the energy spectrum, and taking the ADC values as sampling values.
In some embodiments, after acquiring the plurality of sets of sample values, the fitting unit 222 may fit the sample values to determine the correction information, and the fitting method may include any one or a combination of various data fitting methods such as interpolation, regression, and the like.
In some embodiments, the correction information may be a correction formula, and the parameters included in the correction formula, i.e., the coefficients in the formula, may be determined based on the best fit result.
As shown in FIG. 4, in some embodiments, a theoretical non-linear relationship between gamma energy and output ADC may be used ADC f (E)a,b,c...Fitting the n groups of data obtained by measurement to obtain a plurality of parameters a in the relational expression under the optimal goodness of fit0,b0,c0...。
In some embodiments, the same parameters may be used for multiple photosensors that are consistent in performance; for multiple photosensors that differ in performance, a set of parameters may be determined for each photosensor.
In some embodiments, if all photosensors perform identically, each photosensor may use the fitted nonlinear relationship ADC ═ f (e)a0,b0,c0...(ii) a If the difference exists, each photoelectric sensor (the total number of the detector modules is m photoelectric sensors) is subjected to acquisition and fitting to respectively obtain a0,b0,c0...,a1,b1,c1...,a2,b2,c2...,am-1,bm-1,cm-1.., i.e. m sets of fitting parameters.
As shown in fig. 4, after determining the parameters in the relational expression, the relational expression may be used as a correction formula 410. In some embodiments, the m sets of fitting parameters of all the photosensors obtained above can be used as coefficients of subsequent correction formulas, respectively.
By way of example only, based on the foregoing SiPM detector modules, a single SiPM randomly coupled using the above-described single crystal (assuming uniform characteristics across all SiPMs) uses multiple radiation sources such as 57Co, 133Ba, 22Na, 137Cs with characteristic gamma ray energy peaks of 122keV, 302 and 356keV, 511 and 1275keV, 662keV, respectively. Assuming that N _ ph (E) and h (g) are linear outputs, based on equation 1 in combination with SiPM saturation effect, a correction equation can be obtained, which is shown as equation 2 below:
ADC＝α(1-e-βE) (2)，
wherein alpha and beta are fitting parameters which need to be determined according to sampling values, and e is a natural logarithm. Based on equation 2, a SiPM correction curve 700, as shown in fig. 7, may be obtained, which may be a functional image of equation 2, where the abscissa is the E value and the ordinate is the ADC value.
In some embodiments, the m sets of fitting parameters of all the photosensors obtained above are used as the coefficients of the subsequent correction formula respectively.
In some embodiments, as shown in fig. 4, after the detector starts to operate, the output value obtaining module 210 may obtain the photosensor output value 420, i.e., the ADC value, and the correction value determining module 230 may obtain the correction value 430 of the output value based on the correction formula. In some embodiments, the correction formula may be obtained in advance, or may be obtained after the photosensor output value is obtained.
In some embodiments, the detector module formed by coupling the above-mentioned photosensor array and crystal array corrects the photosensors with signal outputs respectively when detecting radiation events, that is, inputs the output ADC value into the corresponding correction formula to obtain a value obtained by inverse-deducing the correction formula as the correction value ADC' of the ADC value. Assuming that the detector receives radiation photons, m output values (ADC values) ADC are output0，ADC1，ADC2...ADCm-1Inputting the m output values into corresponding correction formulas to reversely deduce to obtain corresponding correction values ADC'0，ADC′1，ADC′2...ADC′m-1。
For example only, based on the foregoing SiPM detector module, equation 2 may be extrapolated backwards to yield the calculation of E, equation 3 shown below:
according to the SiPM correction curve 700 shown in fig. 7, all sipms in the detector modules of the coupled crystal array are subjected to online or offline ADC correction, that is, the ADC value is substituted into formula 3 to obtain a correction value ADC'.
In some embodiments, having acquired the correction value, the spectrum determination module 240 may determine a detector spectrum based on the correction value, the detector spectrum may represent a relationship between an energy value of a radiation photon received by the detector and a count of radiation photons having a corresponding energy value.
As shown in fig. 4, in some embodiments, the correction coefficient determination unit 241 may determine the crystal correction coefficient of the detector based on the correction value.
In some embodiments, the detector may include a plurality of crystals, and the crystal correction factors for each crystal may be different, such that a respective crystal correction factor is determined for each crystal. For each crystal, the correction coefficient determination unit 241 may determine a first crystal energy spectrum based on the correction values, the first crystal energy spectrum representing a relationship between a count of radiation photons received by the crystal and the corresponding correction value.
As shown in fig. 4, in some embodiments, the correction coefficient determination unit 241 may obtain a target map 440 based on the correction value 430, the target map 440 being used to determine the position of the crystal receiving the radiation photons; based on the target profile 440, a first crystal energy profile 450 for each crystal is determined.
In some embodiments, the target map may include a flood map, and the correction coefficient determination unit 241 may determine the correspondence of the correction value to the crystal based on the original map.
In some embodiments, the raw map may be a pre-generated flood map, and the raw map may represent the range of positions of the crystal. The correspondence between the radiation photon and the crystal can be determined based on the crystal position range in the original flood map, and specifically, the coordinate of the radiation photon can be obtained by using an algorithm (e.g., Anger algorithm, etc.) based on the correction value and the corresponding radiation photon count, which crystal position range in the original flood map the coordinate of the radiation photon is located in is judged, and when the coordinate of the radiation photon is located in a certain crystal position range, the coordinate is taken as the crystal corresponding to the radiation photon, that is, the radiation photon received by the detector is associated with the crystal. In some embodiments, the original flood map may be updated using the current coordinate information of the radiation photons, resulting in an updated flood map, which is used as the target map. The target pattern may represent a relationship between a crystal position and a corresponding radiation photon count. For example, as shown in fig. 6A and 6B, the abscissa and ordinate represent the range of crystal positions, the shades of the colors of the regions in the maps 600-1 and 600-2 represent how many the radiation photon counts at the corresponding positions, and in a black background, the darker the color represents the smaller the counts, and the lighter the color represents the larger the counts.
In some embodiments, a Look-Up-Table (LUT) may be generated based on the original map, in which the location range of the crystal is recorded, and the LUT may be searched to determine the crystal corresponding thereto from the coordinates of the radiation photons.
In some embodiments, the raw profile may be generated using various methods (e.g., Anger algorithm, etc.) based on the photosensor output values 420(ADC values) and the radiation photon counts. Radiation photon counting refers to counting of radiation photons received by a detector crystal.
In some embodiments, the target profile may be generated using various methods (e.g., Anger algorithm, etc.) based on the correction values 430 (ADC' values) and the radiation photon counts.
FIG. 8 is a schematic diagram of a target map of SiPMs before and after correction, shown in accordance with some embodiments herein. In some embodiments, as shown in fig. 8, the original map may be a before-SiPM-corrected flow map, i.e., map 800-1, and the target map may be an after-SiPM-corrected flow map, i.e., map 800-2, and it can be seen that the range of crystal positions in the after-correction flow map is relatively clear and accurate.
In some embodiments, correction value ADC 'may be based'0，ADC′1，ADC′2...ADC′m-1And calculating by using methods such as an Anger algorithm and the like to obtain a target spectrum, and then obtaining an energy spectrum of each crystal of the detector module, namely a curve graph taking ADC' as an abscissa and taking the radiation photon count received by a single crystal as an ordinate.
An energy peak may refer to an extreme point of a coordinate within a certain range on an energy spectrum, which may include one or more energy peaks.
As shown in fig. 4, in some embodiments, after acquiring the first crystal energy spectrum 450, the correction coefficient determining unit 241 may acquire an energy value corresponding to an energy peak on the first crystal energy spectrum 450 and a corresponding correction value; a crystal correction factor 460 is determined based on the energy value corresponding to the energy peak and the corresponding correction value.
In some embodiments, the crystal correction coefficient k may be represented by the following equation 4:
k＝E/ADC′ (4)
wherein, E is the energy value corresponding to the energy peak, and ADC' is the correction value corresponding to E.
In some embodiments, a plurality of energy peaks may be selected from the first crystal energy spectrum to obtain a plurality of k values, and the k values are arithmetically averaged or weighted-averaged to obtain the final crystal correction coefficient k. For example, with 22Na as the radiation source, the energy peaks of the characteristic gamma rays of 22Na are known to correspond to energy values of 511keV and 1275 keV. Energy peaks can be selected on the first crystal energy spectrum, theoretically, the energy value corresponding to the energy peak with the largest counting number should be 511keV, the energy value corresponding to the energy peak with the second counting number should be 1275keV, and the two energy values are taken as the energy values E corresponding to the two energy peaks1、E2Then, selecting a correction value ADC 'corresponding to the two energy peaks on the first crystal energy spectrum'1、ADC'2To obtain 2 crystal correction coefficients k1、k2Will k is1、k2The final crystal correction coefficient k is obtained by arithmetic mean or weighted average, etc.
In some embodiments, after determining the crystal correction factor, the spectrum determination unit 242 may determine the detector spectrum based on the crystal correction factor.
As shown in fig. 4, in some embodiments, for each crystal in the detector, the energy spectrum determination unit 242 may determine a second crystal energy spectrum 470 based on the crystal correction factor 460 and the first crystal energy spectrum 450, which may represent a relationship between an energy value of a radiation photon received by the crystal and a count of the corresponding radiation photon.
In some embodiments, the spectrum determination unit 242 may correct each crystal, i.e., correct the first crystal spectrum, using various ways (e.g., linear correction, etc.) based on the crystal correction coefficient, thereby obtaining the second crystal spectrum.
In some embodiments, the correction may be based on a linear correction, e.g., multiplying the correction value (abscissa of the first crystal energy spectrum) by a corresponding crystal correction coefficient, i.e., k ADC' as the energy value of the radiation photon received by the crystal (abscissa of the second crystal energy spectrum); for another example, the product is added with an offset, i.e., k × ADC' + offset, as the energy value of the radiation photons received by the crystal. In some embodiments, the offset may be an empirical value. In some embodiments, two or more energy peaks can be selected from the first crystal energy spectrum, an energy value and a correction value corresponding to each energy peak are obtained, and a k value and an offset are determined according to the energy value and the correction value corresponding to each energy peak. For example, with 22Na as the radiation source, the energy peaks of the characteristic gamma rays of 22Na are known to correspond to energy values of 511keV and 1275 keV. An energy peak can be selected on the first crystal energy spectrum, the energy value corresponding to the energy peak with the largest count is 511keV, the energy value corresponding to the energy peak with the second count is 1275keV, then corresponding correction values are selected on the first crystal energy spectrum, and the k value and the offset are determined according to the energy value and the correction value corresponding to each energy peak. In some embodiments, the k value and the offset may be determined by a linear fitting method based on the energy values corresponding to the plurality of energy peaks and the correction value.
In some embodiments, the crystals may be linearly corrected based on the "true" energy spectrum (e.g., the first crystal energy spectrum) of each crystal. That is, a peak position ADC 'corresponding to a certain energy peak E in the "true" energy spectrum is obtained, a correction coefficient k corresponding to each crystal is calculated as E/ADC', and each crystal is linearly corrected, that is, multiplied by the corresponding correction coefficient, so as to obtain a final energy spectrum (for example, a second crystal energy spectrum) in keV.
As shown in fig. 9A and 9B, in some embodiments, the energy spectrum 900-1 in fig. 9A is a pre-corrected crystal energy spectrum, i.e., an energy spectrum whose abscissa is an ADC value, a first crystal energy spectrum, i.e., an energy spectrum whose abscissa is a correction value ADC', may be generated based on the pre-corrected crystal energy spectrum through a first correction, and then a post-corrected crystal energy spectrum, i.e., a second crystal energy spectrum, whose abscissa is an energy value of a radiation photon may be generated based on the first crystal energy spectrum through a second correction, and the energy spectrum 900-2 in fig. 9B is a post-corrected crystal energy spectrum.
In some embodiments, after acquiring the second crystal energy spectrum of each crystal of the detector, the energy spectrum determination unit 242 may determine the detector energy spectrum based on the second crystal energy spectrum. In some embodiments, the energy spectra of all crystals of the detector may be aggregated as the energy spectrum of the detector.
In some embodiments of the present description, a photoelectric sensor correction formula is determined based on data collected by a detector, an ADC correction value is obtained, and a complex nonlinear relationship of the detector is converted into a nonlinear relationship of the photoelectric sensor, so that the calculation complexity is greatly reduced, and the accuracy requirement of energy calculation of the detector can be satisfied with sufficient accuracy; the relatively accurate corresponding relation between the radiation photon energy and the output value of the detector is obtained through a correction formula, so that the problem of insufficient precision caused by nonlinearity of a photoelectric sensor is solved; the crystal in the detector is further corrected based on the correction value, the quality of the flood map is improved, the resolution is improved, the method can be based on the existing photoelectric sensor correction result, is relatively simple and easy to implement, does not need to be used for independently correcting the crystal sampling, reduces the workload and reduces the complexity; the photoelectric sensor and the crystal are respectively corrected to obtain the energy spectrum of the detector, so that various factors influencing the accuracy of the energy spectrum are considered more comprehensively, the accuracy of the energy spectrum of the detector is improved, the spatial resolution and the energy resolution of the detector are improved, and the examination and treatment of a patient are more accurate and effective; after the energy spectrum is corrected by the detector correction method shown in some embodiments of the present specification, subsequent operations such as scattering recovery, coincidence event determination based on energy window information, TOF information determination, and the like may be performed.
It should be noted that the above descriptions regarding the processes 300, 400 are only for illustration and description, and do not limit the applicable scope of the present specification. Various modifications and changes to the processes 300, 400 may be made by those skilled in the art, guided by the present description. However, such modifications and variations are intended to be within the scope of the present description. For example, step S310 and step S320 may exchange the order.
Having thus described the basic concept, it will be apparent to those skilled in the art that the foregoing detailed disclosure is to be regarded as illustrative only and not as limiting the present specification. Various modifications, improvements and adaptations to the present description may occur to those skilled in the art, although not explicitly described herein. Such modifications, improvements and adaptations are proposed in the present specification and thus fall within the spirit and scope of the exemplary embodiments of the present specification.
Also, the description uses specific words to describe embodiments of the description. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the specification is included. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the specification may be combined as appropriate.
Additionally, the order in which the elements and sequences of the process are recited in the specification, the use of alphanumeric characters, or other designations, is not intended to limit the order in which the processes and methods of the specification occur, unless otherwise specified in the claims. While various presently contemplated embodiments of the invention have been discussed in the foregoing disclosure by way of example, it is to be understood that such detail is solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover all modifications and equivalent arrangements that are within the spirit and scope of the embodiments herein. For example, although the system components described above may be implemented by hardware devices, they may also be implemented by software-only solutions, such as installing the described system on an existing server or mobile device.
Similarly, it should be noted that in the preceding description of embodiments of the present specification, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to imply that more features than are expressly recited in a claim. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.
Numerals describing the number of components, attributes, etc. are used in some embodiments, it being understood that such numerals used in the description of the embodiments are modified in some instances by the use of the modifier "about", "approximately" or "substantially". Unless otherwise indicated, "about", "approximately" or "substantially" indicates that the number allows a variation of ± 20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximations that may vary depending upon the desired properties of the individual embodiments. In some embodiments, the numerical parameter should take into account the specified significant digits and employ a general digit preserving approach. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the range are approximations, in the specific examples, such numerical values are set forth as precisely as possible within the scope of the application.
For each patent, patent application publication, and other material, such as articles, books, specifications, publications, documents, etc., cited in this specification, the entire contents of each are hereby incorporated by reference into this specification. Except where the application history document does not conform to or conflict with the contents of the present specification, it is to be understood that the application history document, as used herein in the present specification or appended claims, is intended to define the broadest scope of the present specification (whether presently or later in the specification) rather than the broadest scope of the present specification. It is to be understood that the descriptions, definitions and/or uses of terms in the accompanying materials of this specification shall control if they are inconsistent or contrary to the descriptions and/or uses of terms in this specification.
Finally, it should be understood that the embodiments described herein are merely illustrative of the principles of the embodiments of the present disclosure. Other variations are also possible within the scope of the present description. Thus, by way of example, and not limitation, alternative configurations of the embodiments of the specification can be considered consistent with the teachings of the specification. Accordingly, the embodiments of the present description are not limited to only those embodiments explicitly described and depicted herein.
Claims (10)
1. A detector calibration method, comprising:
obtaining an output value of the detector, the output value being related to the radiant photon energy value received by the detector;
acquiring correction information, wherein the correction information is used for correcting signal output nonlinearity of a photoelectric sensor of the detector;
determining a correction value for the output value based on the correction information;
based on the correction value, a detector spectrum is determined, the detector spectrum representing a relationship between an energy value of the radiation photon and a count of the radiation photon.
2. The method of claim 1, the obtaining correction information comprising:
acquiring a plurality of groups of sampling values of the detector, wherein each group of sampling values comprises an input energy sampling value and an output sampling value corresponding to the input energy sampling value;
and fitting the plurality of groups of sampling values to determine the correction information.
3. The method of claim 1, the determining a detector spectrum based on the correction value comprising:
determining a crystal correction coefficient for the detector based on the correction value;
determining the detector energy spectrum based on the crystal correction factor.
4. The method of claim 3, the detector comprising a plurality of crystals;
the determining a crystal correction coefficient of the detector based on the correction value comprises:
for each of said crystals, the crystal is,
determining a first crystal energy spectrum based on the correction values, the first crystal energy spectrum representing a relationship between a count of the radiation photons received by the crystal and the corresponding correction value;
acquiring the energy value corresponding to the energy peak on the first crystal energy spectrum and the corresponding correction value;
determining the crystal correction factor based on the energy value corresponding to the energy peak and the corresponding correction value.
5. The method of claim 4, the determining a detector spectrum based on the crystal correction factor comprising:
for each of the crystals, determining a second crystal energy spectrum based on the crystal correction factor and the first crystal energy spectrum, the second crystal energy spectrum representing a relationship between an energy value of the radiation photon received by the crystal and a corresponding count of the radiation photon;
determining the detector energy spectrum based on the second crystal energy spectrum.
6. A detector correction system comprises an output value acquisition module, a correction information acquisition module, a correction value determination module and an energy spectrum determination module;
the output value acquisition module is used for acquiring an output value of the detector, and the output value is related to the radiant photon energy value received by the detector;
the correction information acquisition module is used for acquiring correction information, and the correction information is used for correcting the signal output nonlinearity of the photoelectric sensor of the detector;
the correction value determining module is used for determining a correction value of the output value based on the correction information;
the energy spectrum determination module is to determine a detector energy spectrum based on the correction value, the detector energy spectrum representing a relationship between an energy value of the radiation photon and a count of the radiation photon.
7. The system of claim 6, the correction information acquisition module comprising a sampling unit and a fitting unit;
the sampling unit is used for acquiring a plurality of groups of sampling values of the detector, and each group of sampling values comprises an input energy sampling value and an output sampling value corresponding to the input energy sampling value;
the fitting unit is used for fitting the plurality of groups of sampling values to determine the correction information.
8. The system of claim 6, the power spectrum determination module comprising a correction coefficient determination unit and a power spectrum determination unit;
the correction coefficient determining unit is used for determining the crystal correction coefficient of the detector based on the correction value;
the energy spectrum determination unit is used for determining the energy spectrum of the detector based on the crystal correction coefficient.
9. The system of claim 8, the detector comprising a plurality of crystals;
the determining a crystal correction coefficient of the detector based on the correction value comprises:
for each of said crystals, the crystal is,
determining a first crystal energy spectrum based on the correction values, the first crystal energy spectrum representing a relationship between a count of the radiation photons received by the crystal and the corresponding correction value;
acquiring the energy value corresponding to the energy peak on the first crystal energy spectrum and the corresponding correction value;
determining the crystal correction factor based on the energy value corresponding to the energy peak and the corresponding correction value.
10. The system of claim 9, the determining a detector spectrum based on the crystal correction factor comprising:
for each of the crystals, determining a second crystal energy spectrum based on the crystal correction factor and the first crystal energy spectrum, the second crystal energy spectrum representing a relationship between an energy value of the radiation photon received by the crystal and a corresponding count of the radiation photon;
determining the detector energy spectrum based on the second crystal energy spectrum.
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